The present invention relates to a light-sensitive mixture comprising a naphthoquinonediazidesulfonic acid ester and a binder, which is insoluble in water but is soluble in aqueous alkaline solutions. Such mixtures are particularly suited for preparing printing plates or photoresists.
Mixtures of the foregoing general type and light-sensitive copying materials prepared therefrom are known. Generally, such mixtures contain a naphthoquinonediazidesulfonic acid ester of a monohydric or polyhydric phenol such as a polyhydroxybenzophenone, polyhydroxydinaphthylmethane, polyhydroxydiphenylmethane or 4-(2-phenylprop-2-yl)-phenol.
Amongst these relatively low molecular weight esters, the representatives which have two or more naphthoquinonediazide groups in the molecule are particularly preferred in practice because of their relatively high light-sensitivity, their good developer resistance and the long printing runs obtainable from printing plates prepared therewith. However, many of these compounds, and particularly the preferred representatives having a relatively high content of diazo groups, have the disadvantage that they present an explosion hazard. This means that their preparation, storage and transport must be carried out under very stringent safety precautions and in relatively small portions. So far as possible, the storage and transport of large quantities of such compounds is avoided altogether, and such compounds are, if possible, processed on site and as soon as possible after they are produced.
However, as a result of the considerable world-wide increase in the consumption of positive-action printing plates which have been presensitized with o-quinone diazides, it has been necessary to establish coating plants at an increasing number of sites. It would be desirable if such scattered sites could be supplied with the necessary chemicals from a central point without risk. In the case of naphthoquinonediazidesulfonic acid esters, however, this has become increasingly difficult because of rising safety standards all over the world.
Attempts have been made to solve this problem by mixing the explosive compounds before transport with resins, such as the phenolic resins customarily used in photosensitive coatings, or with other polymeric compounds, but this proposal also requires that the dangerous compound first be prepared and isolated, and handled during mixing. As far as we are aware, no other solutions to this problem have been disclosed. Indeed, the problem itself has hardly been mentioned in the literature.
On the other hand, it is known to prepare and use high molecular weight o-quinone diazides to solve other problems. German Pat. No. 850,860 describes the reaction of o-quinonediazidesulfonyl halides with phenolic resins and the use of the reaction products for coating printing plates, it being necessary to prevent the quinone diazides from crystallizing in the layer. However, the light-sensitivity and other technical properties of these compounds are insufficient for present-day copying and printing requirements.
British Pat. No. 1,113,759 describes polymeric condensation products of pyrogallol with acetone which have been esterified with naphthoquinonediazidesulfonic acids. These products are said to exhibit improved adhesion to aluminum. These products also are much less effective for copying and printing than the low molecular weight naphthoquinonediazidesulfonic acid esters described above.
German Auslegeschrift No. 2,044,868 describes the use of esters formed from naphthoquinonediazidesulfonic acids and polyglycols for preparing photoresist materials. These compounds are said to make the layers less brittle. They have the disadvantage that, because of their oily or soft, resinous consistency, they are difficult to purify. Although they are suitable for use as photoresist materials, they are not sufficiently oleophilic and produce too short a printing run for use in manufacturing offset printing plates.
German Offenlegungsschrift No. 2,146,166 describes naphthoquinonediazidesulfonic acid esters of bisphenol/formaldehyde condensation resins. These compounds also fail to provide technical properties for copying and printing comparable to the initially described low molecular weight naphthoquinone diazides.